The application of films to windows for various purposes is quite common. The films may be applied to any type of window pane for example polymeric or glass panes. Films are applied to window panes for a variety of reasons. For example films can be applied to window panes to affect the ability of these panes to absorb or transmit heat, further films can be applied in order to change the color of a window pane, likewise films can be applied in order to increase the strength of a window pane and in particular the ability of the window pane to stay in tact after an impact by a foreign object. Films are also applied to window panes in order to alter the ability of the window pane to transmit, absorb or reflect visible and invisible solar radiation. It is this latter mentioned area namely the ability of a film to alter the ability of a window pane to transmit solar energy that this invention is primarily concerned. That is this invention is concerned with the interreaction of solar ultraviolet radiation with a solar control window film. More particularly this invention is concerned with window film compositions and constructions whereby the ability of a window pane to transmit solar energy in the ultraviolet and lower visible range is altered by the application of a multilayer composite film to the window pane.
The addition of ultraviolet absorbers to solar control window films in order to alter the ability of a window pane to transmit ultraviolet radiation is known in the prior art. In many instances when an ultraviolet absorber is added to a window solar control film, the resulting overall composite structure, when the film is applied to a window pane has an undesirable yellow hue or tint. This yellow tint or hue originates with the ultraviolet absorber when an effective amount of ultraviolet absorber is added to the window film. In accordance with this invention this yellow hue or tint is eliminated. The objectionable yellow tint or hue may be best described as a slight straw color and is particularly evident in clear films.
The high ultraviolet light absorbing solar control window films, of this invention are useful in environments where ultraviolet rays may degrade the contents of a building or cause health problems for the occupants of these buildings. For example ultraviolet radiation entering a building through its windows will cause carpet and wallpaper to fade. Further the health of the occupants can be affected for example exposure to ultraviolet radiation can cause skin cancer. With this invention, it is possible to eliminate the transmission of solar ultraviolet radiation through a window pane and yet produce a window film which is superior to the prior art films in color.
These ends are accomplished by utilization of an optical brightener in combination with an ultraviolet absorber in a multilayer window treatment film.